Microelectronic devices, such as chips or MEMS, have recently been developed in which at least one antenna is integrated together with other components in a stack of thin layers formed on a semiconducting substrate. It is thus for example possible, in a radio frequency front-end type device, to adapt an antenna directly to a PA circuit (PA for “Power Amplifier”) or an LNA circuit (“LNA” for “Low Noise Amplifier”).
One advantage relating to the production of chip-integrated antennae can be, notably, to reduce the cost of manufacture of the radio frequency microelectronic devices. When directly integrated antennae are formed, it is possible notably to avoid the steps of mounting or assembly of these antennae, and by the same token to avoid certain negative effects relating to this assembly on the electrical performance specifications of the chip. Another advantage relating to this integration is that a number of components external from the chip are eliminated.
Over recent years many short-range systems of communicating objects have been created, using standards such as the “Bluetooth” or “802.11” standard, operating at frequencies on the order of several GHz, for example 2.4 GHz. At the current time it is envisaged, for this type of system of communicating devices, or for applications of the PAN type (PAN for “Personal Area Network”) to use frequencies above those of the abovementioned current standards, for example frequencies of over 10 GHz, or frequencies belonging to another part of the spectrum reserved to ISM (Industrial, Scientific, Medical) applications located around 24 GHz. Use of such ranges of frequencies implies the formation of even smaller antennae than previously, and makes devices with antennae integrated directly in chips even more attractive.
However, chip-integrated antennae have performance specifications inferior to those of external or “free space” antennae. The emission efficiency of an integrated antenna, defined as the ratio of the emitted power of the antenna over the electrical incident power injected into this antenna to provide this emission, is, notably, low compared to that of an antenna in free space, being for example on the order of 10% at 10 GHz or 25% at 20 GHz.
The problem of finding a technique enabling the emission efficiency of chip-integrated antennae to be improved is thus posed.